I just did upgrade vom beta5 to beta6 and now the Header Link Theme Component is no longer working.
All our custom header links are no longer shown in the header.
Looks like something in the new beta has stopped the component from working.
We are now on 2.5.0.beta6 ( b3c8d36412 )
The error log does only show a lot of errors concerning the discourse-locations Plugin but nothing concerning the header problem.